Created attachment 121977 [details]
Krita internal error

Krita crashed when I was editing 2 files and closed one of them. Showing messages like:

Krita: Internal Error
Krita has encountered an internal error:
SAFE ASSERT (krita): "!sanityCheckPointer.isValid()" in file ......KisDocument.cpp, line 545

Clicked Ignore and this message kept popping up. Clicked Abort then Krita crashed silently.

This type of crashes has been happening from time to time and they are responsible for roughly 50% of my data loss using Krita. (The other 50% were caused by Crop/Transform)

I notice a pattern:
1) They only happened when multiple documents are opened in the same session;
2) Contents were copied from the 2nd document to the 1st one;
3) If Krita considers the 2nd document changed (something has to be selected before copying), the "change" was never saved before the error occurred;
4) Error happened either when switching between document tabs, or while saving, or closing the one of them.

Yesterday this error happened to me again and the situation was like:
1) All Krita settings were just deleted minutes ago, 4.2.5 appimage was integrated and used first, only shortcuts were customized, then I removed 4.2.5 and integraed 4.3.0-prealpha (gitb7872b8);
2) I created a new document in that session;
3) I opened an existed document later that session, selected a text shape; pressed Ctrl+C to copy and Ctrl+V to paste it into the first document;
4) I continued to edit in the first document for awhile;
5) I closed the first document, the error occurred. When it happened, the text shape was still selected in the second document.

Hopefully we can hunt this error down someday.